Summary The Whiteshell Air Service Ltd. float-equipped deHavilland DHC-3Otter, C-GGON, serial number225, with one pilot and three passengers on board, departed the Lac du Bonnet, Manitoba, water base at approximately 1100 central daylight time on a day, visual flight rules flight to George Lake. The pilot completed a normal take-off from the Winnipeg River in an easterly direction and began a shallow climb over the shoreline. As the aircraft levelled at approximately 400feet above ground level (agl), there was a loud backfire followed by a complete loss of engine power. The pilot force landed straight ahead; the aircraft struck several large trees and came to rest in a swampy area. The aircraft struck the ground on its left side, both wings broke off, and the engine was buried in the swampy ground. There was no fire. The pilot and one of the passengers were seated in the cockpit and suffered minor injuries. One of the passengers seated in the cabin of the aircraft was thrown clear of the aircraft still strapped in the seat and sustained minor injuries. The other cabin passenger was thrown forward still strapped in the seat, struck the interior structure of the aircraft, and sustained serious injuries. Ce rapport est galement disponible en franais. Other Factual Information On the day before the accident, the aircraft had returned to Lac du Bonnet, Manitoba, with an unusual engine noise. The engine was inspected by the operator's own approved maintenance organization (AMO), and the No.1 cylinder showed signs of excessive blow-by. The cylinder was removed and inspected. The cylinder head was found to be separating from the cylinder barrel. A new cylinder was installed. On the day of the accident, prior to the first flight following the cylinder replacement, a lengthy engine run-up was completed with no anomalies noted. At take-off, the pilot determined that the engine was performing satisfactorily by confirming that the engine's rpm was 2250 at a manifold pressure of 36.5inches. The power output of this type of aircraft engine is checked by measuring the engine rpm at a given manifold pressure. The field barometric pressure is used to establish the manifold pressure. This check requires that the engine rpm be measured at this pressure when the propeller blades are at their low pitch stops. The aircraft manufacturer specifies the rpm at which this occurs. The approved aircraft flight manual for C-GGON indicates that the engine's rpm should range from 2000to 2200rpm when the manifold pressure is equal to the field barometric pressure. The weather at the time of the accident was reported as visual meteorological conditions (VMC) with light winds from the east. The weather at Kenora, Ontario, approximately 75statute miles east, was representative of the area weather and was reported as follows: visibility greater than 15miles; a few clouds at 3700feet agl; temperature 15C; dewpoint 6C; wind 150degrees true at 7knots. The pilot, who was also the owner of the company, held a valid commercial pilot licence. The pilot had extensive flying experience with over 32000flying hours, over 8000hours on type, and 2.7hours in the last 30days. The pilot was also the sole aircraft maintenance engineer (AME) for the company's AMO. The pilot's AME licence had expired in 05October2000 and had not been renewed. The last aircraft inspection was completed by the pilot/AME, after the expiry date of his licence. After the accident, no emergency locator transmitter (ELT) signal was received from the downed aircraft. The ELT had been removed by a company apprentice for re-certification on 08May2003 during an annual inspection of the aircraft. An entry was made in the journey log book stating that the ELT had been removed. Information provided, however, indicated that the pilot of the aircraft was under the impression that a re-certified ELT had been installed in the aircraft in the interim. The Canadian Aviation Regulations (CARs) allow an aircraft to be operated without a serviceable ELT for a period of up to 30days, providing certain conditions are met. One condition is that the operator display a placard in the cockpit noting the removal. Although there was an entry in the log book stating that the ELT had been removed from the aircraft, the aircraft was not placarded to indicate that the aircraft was operating without an ELT. Photo1. A - Insufficient protrusion of adjustment screw B - Excessive valve clearance An examination of the airframe did not reveal any pre-impact anomalies. The engine, a PrattWhitney WaspR-1340-S3H1-G, was removed from the accident site and taken to a local overhaul facility for tear-down analysis. During the rotation of the crankshaft, it was noted that the No.3cylinder exhaust valve did not open. The valve adjustment screw assembly was observed to protrude above the lock nut by 1/16of an inch and the valve clearance was measured at 0.233of an inch. The engine's maintenance manual specifies a minimum protrusion of the valve adjustment screw of 1/8 of an inch and a valve clearance of 0.035 of an inch Photo1). The front engine case was removed and the No.3cylinder exhaust roller was found to be excessively worn. The top portion of the cam roller slot tappet guide had split off and broken. The cam roller was measured and found to be worn 0.249of an inch with a flat spot on one side (AppendixA). The cam ring was inspected and all four exhaust lobes were found to be excessively worn and out of limits. The No.3cylinder exhaust valve push rod was inspected and the ball ends were removed to check for the number of adjustment spacers under the ends. Push rods can be lengthened or shortened by adding spacers underneath the ball ends to accommodate valve adjustments during overhaul or cylinder replacement. Two spacers were noted under one end with one spacer found on the opposite end. The single spacer, however, had been installed standing on end and had been forcibly folded over at a right angle. A review of the aircraft maintenance records indicated that the engine had accumulated a total of 821.1 hours since the last major overhaul by Covington Aircraft Engines Inc. Reportedly, the valve clearances had been checked and adjusted twice since overhaul, once at 100hours and again at 810.7 hours time in service (10.4hours prior to the accident). During both adjustments, no significant anomalies were noted; however, it was not determined whether the No.3exhaust valve had been adjusted. Reportedly, the push rods had not been lengthened or shortened to achieve the required valve clearances. Aircraft maintenance records indicate that the No.3cylinder had not been replaced since overhaul. The valves were adjusted using the Positive Method, as specified in the engine's maintenance manual, to eliminate cam float during the adjustment procedure. The operator's inspection program specifies that the valve clearances are to be checked at 400-hour intervals. It could not be determined when the No.3exhaust valve was last adjusted or when the valve adjustment screw protrusion was set beyond limits. Both cabin passengers were seated in the rearmost row of seats. The seats in the two rows immediately ahead of them had been folded up because they were not in use. The seat structures of both passengers failed. The passenger in the left seat was thrown clear of the aircraft still strapped in his seat through the side door and received only minor injuries. The seriously injured passenger was seated in the right seat. This passenger, still strapped in the seat, was thrown forward violently and seriously injured when he came in contact with the folded seats and other parts of the aircraft's structure. Inspection of the cabin revealed that the seats were all factory-approved installations and were correctly installed. Examination of the crash site revealed that the aircraft experienced high deceleration forces during the crash sequence.